Instrument for preparing an implant support surface and associated method

ABSTRACT

A method and instrument for preparing a surface of a joint is provided. The glenoid surface is adapted for receiving a prosthetic component having a feature closely conforming to the surface. The prosthetic component provides a bearing surface for a head portion of a long bone. The instrument includes a guide having a first feature and a second feature and a tool. The tool is used for cooperation with the first feature for preparing the surface. The first feature is adapted to at least partially control the position of the tool as it prepares the surface. The second feature is adapted to assist in positioning of the guide with respect to the joint.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No. 13/030,219which is a divisional of U.S. Pat. No. 7,927,335, entitled “INSTRUMENTFOR PREPARING AN IMPLANT SUPPORT SURFACE AND ASSOCIATED METHOD”, whichare both herein incorporated by reference in their entireties. Crossreference is made to the following applications: U.S. application Ser.No. 10/951,023 entitled EXTENDED ARTICULATION PROSTHESIS ADAPTOR ANDASSOCIATED METHOD”, U.S. application Ser. No. 10/951,024 entitled“GLENOID AUGMENT AND ASSOCIATED METHOD”, U.S. application Ser. No.10/951,021 entitled MODULAR GLENOID PROSTHESIS AND ASSOCIATED METHOD”,and U.S. application Ser. No. 10/951,022 entitled “GLENOIDINSTRUMENTATION AND ASSOCIATED METHOD”, which are incorporated herein byreference.

TECHNICAL FIELD OF THE INVENTION

The present invention relates generally to the field of orthopaedics,and more particularly, to an implant for use in arthroplasty.

BACKGROUND OF THE INVENTION

During the lifetime of a patient, it may be necessary to perform a totalshoulder replacement procedure on the patient as a result of, forexample, disease or trauma. In a total shoulder replacement procedure, ahumeral component having a head portion is utilized to replace thenatural head portion of the arm bone or humerus. The humeral componentmay include an elongated intramedullary stem which is utilized to securethe humeral component to the patient's humerus. In such a total shoulderreplacement procedure, the natural glenoid surface of the scapula isresurfaced or otherwise replaced with a glenoid component that providesa bearing surface for the head portion of the humeral component. Thehumeral component may be made without a stem or with a short stem.

As alluded to above, the need for a shoulder replacement procedure maybe created by the presence of any one of a number of conditions. Onesuch condition is the deterioration of the patient's scapula in theglenoid surface as a result of, for example, glenohumeral arthritis. Insuch a condition, erosion of the patient's scapula may be observed. Theerosion may be asymmetric, anterior or posterior. Posterior erosion ofon the glenoid surface is particularly common. Such erosion of thescapula renders treatment difficult, if not impossible, with aconventional glenoid prosthesis.

In order to treat a condition in which a portion of the scapula has beeneroded, a number of glenoid prostheses have heretofore been designed.Such glenoid prostheses, known generally as augmented glenoidprostheses, have a posterior edge that is thicker than the correspondinganterior edge.

In FIG. 1, a heretofore-designed augmented glenoid component 1 is shown.The glenoid component 1 has a metallic backing component 5 and plasticinsert 4.

The thickness of the metallic backing component 5 gradually increasesfrom an anterior edge to a posterior edge thereof. The arcuate-shapedmedial surface 2 may over time lead to loosening of the augmentedglenoid component 1, thereby potentially necessitating additionalsurgical procedures to replace or reseat the component 1. Further, dueto the configuration of the medial surface 2, a relatively high shearload is created along the implant-to-bone interface when the component 1is implanted. The presence of a high shear load along theimplant-to-bone interface tends to also cause loosening of the component1 over a period of time. Post-operative loosening is the largest causeof failures of implanted glenoid components.

As shown in FIG. 1, the metal backing may include additional features inthe form of, for example, pegs 6 and center peg 7 to provide additionalsupport of the glenoid implant on the scapula 3.

In FIG. 2 another heretofore-designed augmented glenoid component 8 isshown. The glenoid component 8 has a single component plastic body 9A.The thickness of the plastic body 9A gradually increases from ananterior edge 8A to a posterior edge 8B thereof thereby creating arelatively smooth, arcuate-shaped medial surface 10 from which a numberof posts or pegs 8 extend. The design of this augmented glenoidcomponent 8, however, suffers from at least the same drawbacks as theglenoid component 1.

In FIG. 3 another heretofore-designed augmented glenoid component 11 isshown. The glenoid component 11 also has a single component plastic body11A. The thickness of the plastic body 9B gradually increases from ananterior edge 11A to a posterior edge 11B thereof thereby creating arelatively smooth medial surface 11C from which a keel 12 extends. Thedesign of this augmented glenoid component 11, however, suffers from atleast the same drawbacks as the glenoid components 1 and 8.

Attempts to correct the four mentioned problems with posterior gleniodwear have included the invention of an augmented glenoid component witha step support face with the step support face being posterior. Such anaugmented glenoid component is much more fully described in U.S. Pat.No. 6,699,289 to Iannotti et al issued Mar. 2, 2004. Hereby incorporatedin its entirety by reference.

The augmented gleniod component of U.S. Pat. No. 6,699,289 requires astepped pocket or locating surface for the augmented glenoid component.Such a stepped surface is very difficult to create. Certain processesfor preparing the glenoid fossa for such a component can consist merelyof hand or power tools, which are manually guided to prepare the cavityfor receiving the augmented glenoid component.

What is needed therefore is a surgical procedure and instrumentation toovercome one or more of the afore mentioned problems.

SUMMARY OF THE INVENTION

According to the present invention, an instrument and method forperforming surgery is provided, which includes the careful preparationof the bone surface for preparing a posterior augmented glenoid. Thepresent invention includes a device to produce a geometry of a complexnature for an implant surface when irregular bone loss has occurred andan augmented implant component is advised.

According to the present invention, a device and technique are providedby which the surgeon can mill the glenoid surface in a bone preservingfashion. A step is created in the glenoid fossa that replicates thebackside surface of an augmented step glenoid implant such as that ofU.S. Pat. No. 6,699,289. The instrumentation may include a rotating millwith a sleeve that has a fixed pivoting axis to create a cylindricalshape in the posterior aspect of the eroded glenoid fossa. This mill,with the pivoting axis, engages a guide that prescribes or limits theproper depth for the step. This guide can be instructed in many waysthat permit the mill to plunge into the posterior glenoid and then pivoton its axis while milling the bone. The device is used to create acylindrical step in the glenoid so that the glenoid implant can be fullysupported.

This step glenoid of the glenoid implant and underlying bony supportpermits forces to be transmitted to the scapula in a manner that greatlyreduces sheer. By reducing the risk of high sheer it is believed theimplant will be more stable and less likely to result in loosening andfailure.

According to the present invention, two distinct devices may work inconcert to create a desired step geometry for the augmented step glenoidimplant. The first of these devices is a milling device with a cuttinghead that embodies a specific shape matching the cross-sectional shapeof the step portion of glenoid implant. The milling device is connectedto a shaft for attachment to a power driven device such as a drill.Around the cutting head is a sleeve that has a pivoting axis at aspecific position on the shaft such that when the cutting head is fullyextended from the shaft, the cutting head is at a fixed known positionrelative to the pivoting axis. This permits a reproducible cylindricalgeometry to be milled into the bone. Alternatively, the cutting head andsleeve may not move relative to each other and the cutting head may bein a fixed relationship with the pivoting axis on the sleeve.

The other device is a positioning jig that permits the surgeon toaccurately place in a reproducible manner the milling device such thatthe mill removes only the bone necessary to match a glenoid implant tothe patients condition. This jig defines a depth of cut as well asaccurately positioning the cutter so that the device mills the bonelongitudinally along the axis of the glenoid fossa. Only the posterioreroded bone is resurfaced to a defined shape matching the implant. Thejig may accomplish this task while only permitting the rotation of thepivoting axis defined on the mill sleeve. The translation of the milldevice may be permitted in a medial lateral direction. An end stopdefines the depth of the step relative to the reamed anterior portion ofthe glenoid fossa.

The two devices function together to create a reproducible geometry onthe glenoid where posterior bone loss exists permitting the use of aposterior augmented glenoid implant.

According to one embodiment of the present invention, there is providedan instrument for preparing a surface of a joint. The surface is adaptedfor receiving a prosthesis component having a feature closely conformingto the surface. The prosthesis component provides a bearing surface fora portion of a long bone. The instrument includes a guide having a firstfeature and a second feature and a tool. The tool is used forcooperation with the first feature for preparing the surface. The firstfeature is adapted to at least partially control the position of thetool as it prepares the surface. The second feature is adapted to assistin positioning of the guide with respect to the joint.

According to another embodiment of the present invention there isprovided an instrument for preparing a feature on a scapula. The featureis adapted for receiving an augmented glenoid component for providing abearing surface for a head portion of a humerus. The instrument includesa guide defining a guiding feature and a locating feature and a tool.The tool is used for cooperation with the guiding feature for preparingthe feature. The guiding feature is adapted to at least partiallyguiding the tool as it prepares the glenoid surface. The locatingfeature is adapted to assist in locating the guide with respect to thescapula.

According to still another embodiment of the present invention there isprovided an instrument kit for use in preparing a glenoid of a scapula.The glenoid is adapted for receiving a glenoid component having afeature closely conforming to the glenoid. The glenoid componentprovides a bearing surface for a head portion of a humerus. Theinstrument kit includes a first portion tool for preparing a firstportion of the glenoid of a scapula and a second portion tool assemblyfor preparing a second portion of the glenoid of a scapula. Asubstantial portion of the second portion tool is spaced from the firstportion.

According to a further embodiment of the present invention, there isprovided a method for performing arthroplasty on a glenoid. The methodincludes the steps of determining a reference location on the glenoidand preparing a location feature in the glenoid corresponding to thereference location. The method also includes the steps of providing acutting guide, securing the cutting guide to the location feature, andproviding a cutter. The method also includes the steps of preparing acavity in the glenoid with the cutter, using the cutting guide to atleast partially control the position of the cutter as it prepares thecavity. The method further includes the steps of providing a glenoidimplant and implanting the glenoid implant onto the cavity.

The technical advantages of the present invention include the ability toreproduce the complex geometry in a glenoid to replicate and support aposterior augmented glenoid. For example, according to one aspect of thepresent invention, an instrument kit for preparing a glenoid scapula isprovided. The glenoid is adapted for receiving a glenoid componenthaving a feature closely forming to the glenoid. The glenoid componentprovides a bearing surface for a head portion of a humerus.

The instrument kit includes a first portion tool for preparing a firstportion of the glenoid and a second portion of the glenoid. Asubstantial portion of the second portion is spaced from the firstportion. The second portion tool assembly includes a guide having afirst feature and a second feature and a second portion tool. The secondportion tool cooperates with a first feature for preparing the secondportion of the glenoid. The first feature is adapted to at leastpartially to control the position of the second portion of the tool asprepares the second glenoid surface. The guide and tools provides areproducible complex geometry. Thus, the present invention provides fora reproducible complex geometry and a glenoid to replicate and supportthe posterior augmented glenoid.

The technical advantages of the present invention, further include theability to produce a support surface to support a glenoid that transmitsforces normally to the articulating surface. The normal support resultsin less shear, greater stability and less likelihood of the glenoidprosthesis to loosen. For example, according to another aspect of thepresent invention, an instrument kit is provided with a first portiontool for preparing a first portion of the glenoid and a second portiontool for preparing a second portion of the glenoid. The second portiontool cooperates with the first feature prepared by the first portiontool. The guide includes a base and a restraining component to guide thetool in a position normal to the articulating surface. Thus, the presentinvention provides for a support surface to support a glenoid thattransmits forces normally to the articulating surface.

The technical advantages of the present invention further include theability to remove only bone that is necessary to match the implant. Forexample, according to yet another aspect of the present invention, aninstrument kit is provided for preparing a glenoid of a scapulaincluding a first portion tool for preparing a first portion of theglenoid and a second portion tool assembly. The second portion toolassembly is supported by the surface prepared by the first portion tool.The second portion tool assembly includes a rotatable tool and acylindrical tube surrounding the tool. The cylindrical tube is pivotallyattached to a bearing to provide a shape similar to that of theposterior augmented portion of the posterior augmented glenoid. Thus,the present invention provides for the removal of only the bonenecessary to match the implant.

The technical advantages of the present invention, further include theability of the jig to define the depth of cut for preparing the glenoidsurface. For example, according to one aspect of the present invention,an instrument kit is provided including a first portion tool forpreparing a first portion and a second portion tool assembly including aguide supported by the surface prepared by the first portion tool and asecond portion tool for cooperating with the guide. The guide and thesecond portion tool act in concert to define the depth of cut. Thus, thepresent invention provides for a jig that can define the depth of cut.

The technical advantages of the present inventions further include theability of the instrument to accurately position the cutter. Forexample, according to yet another aspect of the present invention, aninstrument kit is provided with a first portion tool and a secondportion tool assembly including a guide supported by the surfaceprepared by the first portion tool. The second portion tool assemblyincludes a guide having a base and a restraining component. Therestraining component restrains the second portion tool to provide foran accurate position of the cutter. Thus, the present invention providesfor a guide for accurately positioning the cutter.

The technical advantages of the present invention, further include theability of the instrument of the present invention to be used for rightand left hand shoulders. For example according to a further of thepresent invention, the instrument kit includes a guide, which may besymmetrically designed. By being symmetrically designed, the guide maybe used for both right and left-hand shoulders. Thus, the presentinvention, provides for an instrument that can be used for right andleft hand shoulders.

The technical advantages of the present invention, further include theability of the instrument to be used for all sizes and shapes of glenoidimplants. For example, according to yet another aspect of the presentinvention, the instrument includes a first portion tool for preparing afirst portion of the glenoid and a second portion tool including a guidebeing supported by the surface prepared by the first portion tool and asecond portion tool to be constrained by the guide. The guide may bemodular or may include an internal component or bushing to provide fordifferent diameters of the second portion tool. Similarly, the firstportion tool may be provided with different sizes to provide for avariety of glenoid implants. Thus, the present invention provides for aninstrument that may be used for all sizes of glenoid implants.

Other technical advantages of the present invention will be readilyapparent to one skilled in the art from the following figures,descriptions and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side sectional view of a prior art augmented glenoidcomponent;

FIG. 2 is a side sectional view of another prior art augmented glenoidcomponent;

FIG. 3 is a side sectional view of another prior art augmented glenoidcomponent;

FIG. 4 is a perspective view showing an augmented glenoid component foruse in a cavity prepared by the cutting tool of the present invention;

FIG. 5 is another perspective view of the augmented glenoid component ofFIG. 4;

FIG. 6 is an end view of the augmented glenoid component of FIG. 4;

FIG. 7 is an bottom view of the augmented glenoid component of FIG. 4;

FIG. 8 is an side view of the augmented glenoid component of FIG. 4;

FIG. 9 is a side view partially in cross section of a natural glenoidfossa with posterior erosion;

FIG. 10 is a side view partially in cross section of a natural glenoidfossa with a portion machined for receiving a prior art glenoidcomponent;

FIG. 11 is a side sectional view of a prior art augmented glenoidcomponent in position on a prepared glenoid fossa;

FIG. 12 is a side view partially in cross section of another naturalglenoid fossa with posterior erosion;

FIG. 13 is a side view partially in cross section of the natural glenoidfossa with posterior erosion of FIG. 12 with an alignment pin inposition in the glenoid;

FIG. 14 is a side view partially in cross section of the natural glenoidfossa with posterior erosion with an alignment pin of FIG. 13 showing anend mill in contact with the glenoid fossa preparing a surface accordingto an embodiment of the present invention;

FIG. 15 is a side view partially in cross section of the glenoid fossawith posterior erosion showing the surface prepared by the end mill ofFIG. 14 and showing a drill guide for preparing a glenoid component peghole according to an embodiment of the present invention in position onthe surface prepared by the end mill of FIG. 14;

FIG. 16 is a side view partially in cross section of the glenoid fossawith posterior erosion showing cutting guide for use in preparing amounting pocket for a posterior augmented glenoid component with thedrill guide aligned to the peg hole prepared by the drill guide of FIG.15 according to an embodiment of the present invention;

FIG. 17 is an end view of the cutting guide and glenoid fossa of FIG.16;

FIG. 18 is a side view partially in cross section of the glenoid fossawith posterior erosion showing the mounting pocket prepared using thecutting guide of FIG. 16 and showing a second drill guide for preparinga second glenoid component peg hole according to an embodiment of thepresent invention in position on the surface prepared by the end mill ofFIG. 9;

FIG. 19 is an exploded side view partially in cross section of theglenoid fossa with posterior erosion showing the mounting pocketprepared using the cutting guide of FIG. 16 and two peg holes preparedusing the drill guides of FIGS. 15 and 17 and showing a glenoidcomponent in position above the prepared surface according to anembodiment of the present invention;

FIG. 20 is a perspective view of the base of the cutting guide of FIG.16 according to an embodiment of the present invention;

FIG. 21 is another perspective view of the base of FIG. 20;

FIG. 22 is a perspective view of a cutting tool for use in preparing themounting pocket for the posterior augmented glenoid component of FIG. 19and a cut-away partial perspective view of the restraining component ofthe cutting guide for use with the base of FIG. 20 to form the cuttingguide of FIG. 16 according to an embodiment of the present invention;

FIG. 23 is another perspective view of the cutting tool and restrainingcomponent of FIG. 22 according to an embodiment of the presentinvention;

FIG. 24 is yet another perspective view of the cutting tool andrestraining component of FIG. 22 according to an embodiment of thepresent invention showing the cutting tool in the retracted position;

FIG. 25 is still another perspective view of the cutting tool andrestraining component of FIG. 22 according to an embodiment of thepresent invention showing the cutting tool in the extended position;

FIG. 26 is a perspective view of another embodiment of a base for thecutting guide of FIG. 16 with an outboard support;

FIG. 27 is a plan view partially in cross section of a kit for use inperforming shoulder arthroplasty in accordance with another embodimentof the present invention;

FIG. 28 is an exploded perspective view of glenoid vault of a scapula, ahumerus, and an augmented glenoid for use in the cavity of a glenoidprepared with the instruments of the present invention; and

FIG. 29 is a perspective view of a cutting tool assembly according toanother embodiment of the present invention;

FIG. 30 is a perspective view of the cutting total assembly of FIG. 29;

FIG. 31 is an exploded perspective view of the cutting tool assembly ofFIG. 29;

FIG. 32 is a perspective view of a cutting guide for use with thecutting assembly tool of FIG. 29 is accordance to an embodiment of thepresent invention;

FIG. 33 is a flow chart of a method for performing shoulder arthroplastyin accordance with yet another embodiment of the present invention; and

FIG. 34 is plan view of a cutting tool assembly for use on a tibia forpreparing a tibia for a knee prosthesis according to another embodimentof the present invention.

Corresponding reference characters indicate corresponding partsthroughout the several views. Like reference characters tend to indicatelike parts throughout the several views.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention and the advantages thereof are bestunderstood by referring to the following descriptions and drawings,wherein like numerals are used for like and corresponding parts of thedrawings.

Referring now to FIG. 4-8, the glenoid component 20 is shown, which maybe used in the cavity prepared by the instrument of the presentinvention. The glenoid component 20 is in the form of an augmentedglenoid and may, as shown in FIG. 4-8 include a buttress 22 separating afirst mounting surface 24 from a second mounting surface 26. The glenoidcomponent 20 may include an articulating surface 28 positioned opposedto the mounting surfaces 24 and 26.

The augmented glenoid component 20 may include additional features tohelp secure the glenoid component 20 to the scapula. For example, thefirst mounting surface 24 may include first pegs 30 extending from themounting surface 24 as well as a central peg 32. The second mountingsurface 26 may also include pegs 30 for extending from the mountingsurface 26. The second mounting surface and the articulating surface 28define a posterior augment 36 positioned between the mounting surface 26and the articulating surface 28. The posterior augment 36 providessupport for the posterior erosion of the glenoid.

Referring now to FIG. 9, natural glenoid 38 of scapula 40 is shown. Thenatural glenoid 38 includes a portion 3 of the scapula 40 with a surface42 describing posterior erosion.

Referring now to FIG. 10, the scapula 40 is shown with a first milledsurface 44 extracted from the natural glenoid 38 and a pocket 46machined with the instruments of the present invention shown removingthe posterior erosion surface 42. The machined glenoid surface 44 andthe pocket 46 may be prepared utilizing the instruments of the presentinvention.

Referring now to FIG. 11, the glenoid component 20 of FIGS. 4-8 is shownin position above on the pocket 46 and glenoid surfaces 44 prepared bythe instruments of the present invention. As can be shown in FIG. 11,the force F from the patient may be supported by resistance forces R1and R2 extending from the prepared glenoid surface 44 and the pocket 46respectively. As can be seen in FIG. 11, the forces R1, R2, and F areall collinear. Thus, the instrument of the present invention providesfor a posterior augmented glenoid 20, which provides for normal forcesand minimizes shear forces to provide for less shear and a more stableglenoid implant that is less likely to loosen during use.

Referring now to FIG. 12, a glenoid fossa of a scapula 40 is shown. Theglenoid fossa 38 includes a posteriorly eroded surface 42 with thehealthy glenoid surface shown in phantom as surface 48.

According to the present invention and referring now to FIG. 13-19,instrumentation and a corresponding method are shown for preparing animplant support surface for a glenoid implant.

According to the present invention and referring now to FIG. 13, analignment pin 100 is shown in position in the scapula 40. The alignmentpin 100 may include, for example, a point or cutting edge 102 for use incutting bone in the installation process of the alignment pin 100. Thealignment pin 100 may further include external threads 104 for assistingin the insertion of the alignment pin 100. The alignment pin 100 may bea part of an instrument set 101.

The alignment pin 100 may be positioned in the glenoid fossa 38 of thescapula 40 in any suitable manner. For example, the alignment pin 100may be manually inserted. The alignment pin may be inserted by hand orwith the use of, for example, a power tool, for example, a drill 106.The alignment pin 100 may be positioned manually or may as shown in FIG.13, may be guided by, for example, guide 108 that is positioned againstouter surface 110 of the scapula 40. It should be appreciated that thatalignment pin 100 may be inserted using diagnostic techniques such thatusing a fluoroscope or may alternatively be positioned using computeraided surgical devices. For example, and as shown in FIG. 13 thealignment pin 100 may be centrally positioned in the glenoid fossa 38.The guide 108 and the drill 106 may also be part of the instrument set101.

According to the present invention and referring now to FIG. 14, a firstportion tool 110 in the form of, for example, an end mill is shown. Theend mill 110 includes a cutter 112 to which shank 114 is attached. Theend mill 110 includes the central opening 116. The central opening 116is sized for sliding engagement with alignment pin 100. The end mill 110may also be part of the instrument set 101.

As shown in FIG. 14, the end mill 110 is positioned above the glenoidfossa 38 and the alignment pin 100 is engaged with opening 116 toadvance the end mill 110 in the direction of arrow 118 until cuttingedge 120 of the cutter 112 engages with the glenoid fossa 38. Thecutting edge 120 is utilized to form first portion 122 of preparedsurface 124. The first portion 122 of the prepared surface 124 may haveany shape. For example, and as is shown in FIG. 14, the first portion122 of the prepared surface 124 may have a shape defined by cutting edge120 of the cutter 112. While the cutter 112 may have any suitable shape,for simplicity and is shown in FIG. 14, the cutter 112 has a cuttingedge 120 defined by a radius R extending from origin 126. The cuttingedge 120 thus is convex and may be, as shown in FIG. 14, a portion of asphere. When machined by the cutting edge 120 of the cutter 112 of FIG.14, the first portion 122 is generally concaved.

The end mill 110 may be manually rotated in the direction of arrow 128by any suitable method. For example, the end mill 110 may be manuallyrotated or rotated by a tool in the form of, for example, a drill 106.Preferably and is shown in FIG. 14, the glenoid fossa 38 of the scapula20 is machined until the entire concave portion 122 is a preparedsurface.

According to the present invention and referring now to FIG. 15, a guidein the form of first drill guide 130 is shown as part of the instrumentset 101 of the present invention. The first drill guide 130 is utilizedafter the concave first portion 122 has been prepared by the firstportion tool 110 of FIG. 14.

The first drill guide 130 includes a base 132 having a contact surface134 for contact with the prepared surface 122 of the scapula 40. Thelocating surface 134 preferably has the shape closely conform with theprepared surface 122. Thus, the contact surface 134 is preferablygenerally convex.

As shown in FIG. 15, the first drill guide 130 further may include anopening 136 for cooperation with alignment pin 101. The opening 136 issized for slideably fitting the alignment pin 100. First drill guide 130is installed onto the scapula 40 by advancing the first drill guide 130in the direction of arrow 138 until the opening 136 of the base 132 isin alignment with alignment pin 100 with which the first drill guide 130is thereby aligned. The alignment pin 100 is slidably fitted to opening136 of the first drill guide 130. The first opening 136 of the drillguide 136 is then mated with the alignment pin 100 until convex surface134 of the base 132 is seated against the prepared surface 122 of thescapula 40. In this position the first drill guide 130 is seated inlocation for its use.

The first drill guide 130 further includes a guiding feature 140 in theform of, for example, bushing or opening for receiving a drill. Itshould be appreciated and shown in FIG. 15, that the first drill guide130 may include a handle 142 for assisting in the proper positioning ofthe first drill guide 130 against the scapula 40.

After the first drill guide 130 is in position against the scapula 40, afirst peg tool 144 in the form of, for example, a drill is fitted intodrill guide 140 and advanced downwardly in the direction of arrow 138forming first peg opening 146 in the scapula 40. A stop 148 may bepositioned on the drill 144 for seating against the base 132 to limitthe downward motion of the drill 144 and thus set the proper depth forthe opening 146.

Once the opening 146 has been prepared in the scapula 40, the firstdrill guide 130 may be removed from the glenoid fossa 38. At this pointalignment pin 100 may also be removed from the glenoid fossa 38.

According to the present invention and referring now to FIG. 16, theinstrument set 101 of the present invention may further include aninstrument 150 for preparing a mounting pocket 152 posteriorly in thescapula 40. The posterior pocket preparing instrument 150 as shown inFIG. 16 includes a guide in the form of cutting guide 156 as well as, atool in the form of, as shown in FIG. 16, of a milling cutter 158. Theinstrument 150 is utilized to prepare the glenoid surface or mountingpocket 152 of the scapula 40. The glenoid surface or mounting pocket 152is adapted for receiving a glenoid component having a feature closelyconforming to the glenoid surface. The glenoid component may be forexample, glenoid component 20, as shown in FIGS. 4-8, and may provide abearing surface for the head portion of a humerus.

The cutting guide 156 includes a first feature 160 in the form of aguiding feature adapted to at least partially control the position ofthe tool 158 as it prepares the mounting pocket 152. As shown in FIG.16, the cutting guide 156 further includes the second feature 162. Thesecond feature 162 is adapted to assist in positioning of the cuttingguide 156 with respect to the scapula 40.

The first feature or guiding feature 160 may have any suitable size,shape and configuration for guiding the tool 158 to prepare the mountingpocket 152. For example and as is shown in FIG. 16, the guiding feature160 may be defined by a wall 164 in the guiding feature for forming acylindrical opening 166. The wall 164 may form a hollow cylinder 168.Alternatively, the wall 164, the opening 166, and cylinder 168 mayconstrain the tool or the cutter 158.

The first feature or guiding feature 160 may be moveable with respect tothe cutting guide 156. For example, the cylinder 168 as shown in FIG. 16may rotate relative to the cutting guide 156 in the direction of thearrows 170.

The guiding feature or first feature 160 may as shown in FIG. 16,include a bearing 172. The bearing 172 may include a post 174 extendingoutwardly from base 176, of the cutting guide 156. The bearing 172 maybe in the form of a journal bearing or in the form of a trunnion. Thecylinder 168 may pivot about the bearing 172 to prepare the mountingpocket 152.

The bearing 172 may define a bearing centerline 178 about which the tool158 is pivotally attached. The centerline 178 may, as shown in FIG. 16,be generally parallel to the base 176. As shown in FIG. 16, the cuttingguide 176 may further include a handle 180 for supporting and guidingthe cutting guide 156.

The second feature or position feature 162 may have any suitable shapeor form capable of positioning the cutting guide 156 with respect to thescapula 40. For example and is shown in FIG. 16, the cutting guide 156may include a mounting surface 182 formed in base 176 of the cuttingguide 156. The mounting surface 182 preferably and is shown in FIG. 16,has a shape compatable with the prepared surface 122 of the scapula 40.For example and is shown in FIG. 16, the mounting surface 182 isgenerally convex and may, for example, have a generally hemisphericalshape.

The positioning feature 162 may in addition to the mounting surface 182include a protrusion in the form of, for example, a pin 184. The pin 184extends outwardly from mounting surface 182 of the base 176 of thecutting guide 156. The pin 184 may be generally cylindrical and adaptedfor a sliding fit within opening or peg hole 146 formed in the scapula40.

The cutting guide 156 is installed by grasping the handle 180 andadvancing the cutting guide 156 toward the scapula 40 in the directionof arrow 186. The pin 184 is aligned with peg hole 146 and the cuttingguide 156 is advanced until the mounting surface 182 sits againstprepared surface 122 of the scapula. Once the cutting guide 186 sits inposition, the tool in the form of, for example, milling cutter 158, isadvanced toward the scapula 40 in the direction of arrow 188 until themilling cutter 158 is in a full depth position. After the milling cutter158 is at its full depth, the milling cutter 158 is rotated aboutbearing 172 in the direction of arrows 170 about axis 178 until themounting pocket 152 is fully prepared. After the mounting pocket 152 isfully prepared, the cutting guide 156 is removed from the scapula 40.

The tool or milling cutter 158 may be rotated by any suitable method forexample, milling cutter 158 may be manually rotated, or preferably, maybe rotated by use of a power tool, for example, by drill 106.

Referring now to FIG. 17, it should be appreciated that cutting guide156 may be further secured by additional features to secure the cuttingguide 156 to the scapula 40. For example and is shown in FIG. 17,mounting screws, for example, first mounting screw 190 and secondmounting screw 192 may be secured through openings 194 in the base 176of the cutting guide 156. The mounting screws 190 and 192 are used toavoid requiring the holding of the cutting guide 156 in place manuallywhile the mounting pocket 152 is prepared.

Referring now to FIG. 18, optional features may be prepared in thescapula 40 for preparing the scapula 40 for receiving the glenoidimplant for example, glenoid implant 20 of FIGS. 4-8. For example and isshown in FIG. 18, a second drill guide 196 may be utilized as a part ofthe instrument set 101. The second drill guide 196 is used to preparesecond peg hole 198 for receiving the second peg (not shown) of theglenoid component 20 of FIGS. 4-8.

The second drill guide 196 may have any suitable size, shape, andconfiguration capable of guiding a tool, for example, a second drill 200for preparing the second peg 198. The second drill guide 196 may, forexample, include a base 202 and may include a handle 204 extending fromthe base 202 for assisting in positioning and securing the second drillguide 196 against the scapula 40.

The second drill guide 196 may include a positioning feature 162 in theform of, for example, mounting surface 206. The mounting surface 206 maybe formed on base 202. The mounting surface 206 is adapted forpositioning the base 202 against prepared surface 122 of the scapula 40.The mounting surface 206 is preferably closely conforming to theprepared surface 122 and may, as shown in FIG. 18, be generally convex.The mounting surface 206 may, as shown in FIG. 18, be generallyhemispherical.

The positioning feature 162 of the second drill guide 196 may furtherinclude a peg hole alignment feature in the form of, for example, a peghole alignment pin 208. The peg hole alignment pin 208 may be generallycylindrical in shape for close conformance to first peg hole 146 formedin the scapula 40.

The second drill guide 196 may further include a guiding feature 210used in guiding the second drill 200 when preparing the second peg hole198. The guiding feature 210 may as shown in FIG. 18, be in the form ofa bushing or a cylindrical opening formation base 202 of the drill guide196. The bushing 210 may be generally cylindrical and have a shapegenerally conforming to and providing rotating clearance for the seconddrill 200.

When installing the second drill guide 196 into the scapula 40, thesecond drill guide 196 is advanced in the direction of arrow 212. Thesecond peg alignment pin 208 is aligned with the second peg hole 146 andthe second drill guide 196 is advanced in the direction of 212 until themounting surface 206 of the base 202 of the drill guide 196 is seatedsecurely prepared surface 122 of the scapula 40. After the drill guide196 is properly seated against the scapula 40, the second drill 200 isadvanced downwardly in the direction of arrow 212 until the second drill202 is fully seated in the scapula 40 and the second peg hole 198 isproperly prepared.

The second drill guide 196 may optionally include a feature forcontrolling the depth of the second drill 202 and the correspondingdepth of the second peg hole 198. For example and as is shown in FIG.18, the depth control feature may be in the form of the stop 214positioned on the second drill 202. The second drill 202 may be advanceddownwardly in the direction of arrow 212 until the stop 214 sits againstthe base of the second drill guide 196. After the second peg hole 198 isfully prepared, the second drill guide may be removed from the scapula40.

Referring now to FIG. 19, the glenoid component 20 is shown in positionabove the mounting pocket 152 prepared by the instrument set 101 of thepresent invention. As can readily be seen in FIG. 19, the preparedsurface 122 of the mounting pocket 152, as well as, the first peg hole146 and the second peg hole 198 formed in the scapula 40 are adapted toprovide for a proper seat of the glenoid component 20. For example, thefirst prepared surface 122 closely conforms to the first mountingsurface 24 of the glenoid component 20. The mounting pocket 152 closelyconfirms to the mounting surface 26 of the glenoid component 20.Further, the first peg hole 146 in the scapula 40 closely conforms insize and position to the first peg 34 of the glenoid component 20.Similarly, the second peg hole 198 has a size, shape, and position tomatingly receive the central peg 32 of the glenoid component 20.

To assemble the glenoid component 20 onto the scapula 40, the glenoidcomponent 20 is advanced downwardly in the direction of arrow 216 untilthe pegs 32 and 34 align with the first peg hole 146 and the second peghole 198, respectively. The glenoid component 20 is then furtheradvanced in the direction of arrow 216 until the mounting surface 24seats against the prepared surface 122 of the scapula and until themounting surface 26 seats against the mounting pocket 152 of the scapula40.

It should be appreciated that the instrument 100 as described in FIGS.13-18 include only two holes being formed in the scapula 40 andappreciated that the glenoid component 20 of FIGS. 4-8 include fourfirst pegs 34. It should be appreciated that the glenoid component 20may include only one first peg 34 as shown in FIG. 19 or alternativelythe first drill guide of claim 15 or the second drill guide 196 of FIG.18, may be include additional bushing for receiving a drill forpreparing the holes for receiving the additional pegs for the glenoidcomponent 20.

Referring now to FIGS. 20 and 21, the cutting guide 156 of theinstrument set 101 is shown in greater detail. The cutting guide 156includes a base 176, which defines mounting hole 194 for passing themounting screw 190 therethrough. Base 176 may further include a firstthreaded opening 216 for use with the right shoulder and a secondthreaded opening 218 with use with a left shoulder. The use of the twothreaded holes 216 and 218 permits the cutting guide 156 to besymmetrical and therefore to be useable for both the right shoulder andthe left shoulder. Base 176 further includes the mounting surface 182which, as is shown in FIGS. 20-21, may be convex.

The cutting guide 156 further includes the guiding feature 160 as wellas the locating feature 162. The guiding feature 160 may include thefirst post 174 in which the bearing or trunnion 172 is formed. As shownin FIGS. 20 and 21, the guiding feature 162 may include a second post220 extending spaced from and parallel to the first post 174. The secondpost 220 includes a second post bearing 222, which is parallel andspaced from the first bearing 172. It should be appreciated that asolitary post 174 may be sufficient if the post 174 has a bearing ofsufficient width to adequately support the cutter 158 (see FIG. 16).

The locating feature 162 may be in the form of, as shown in FIGS. 20 and21, the mounting surface 182, as well as, the additional features in theform of, for example, the first peg hole alignment 184. It should beappreciated that the locating feature 162 may further include a secondpeg hole alignment pin 224 spaced from the first peg hole alignment pin184. Pin 224 also extends from the mounting surface 182.

Referring now to FIGS. 22-25, cutting tool assembly 226 of theinstrument set 101 is shown. The cutting tool assembly 226 includessheath or housing 168. The sheath 168 is generally cylindrical andhollow. A milling cutter body 228 is rotatively fitted within the sheath168. The milling cutter 158 extends from distal end 230 of the body 228.The body 228 is slideably positioned along the shaft portion 232 of stem234. The body 228 is at least partially hollow for receiving the shaftportion 232 of the stem 234. A spring 236 may be utilize to urge sheath168 distally in the direction of arrow 238 to protect the milling cutter158. The spring 236 cooperates with shoulder 240 to urge the sheath 168in the direction of arrow 238. A connector 242 is positioned proximallyon the stem 234 for cooperation with a tool, for example, a drill 106 todrive or rotate the milling cutter 158.

The milling cutter 158 may have any suitable shape and may, as shown inFIGS. 22-25, include a plurality of flutes 244, which include cuttingedges 246. Any number of plurality of flutes 244 may be utilized. Forexample and is shown in FIGS. 22-25, four equally spaced apart flutes244 may be utilized. As shown in FIGS. 22-25, the milling cutter 158 mayinclude internal openings 248 to provide a collection point for themachined bone.

Referring now to FIGS. 24 and 25, the cutting tool assembly 226 may besecured to the bearing 172 of the cutting guide 156 (see FIG. 16) in anysuitable manner. For example and as is shown in FIGS. 24 and 25, thecutting tool assembly 226 is supported by pivoting support 250. Thepivoting support 250 may have any suitable size and shape and may asshown in FIGS. 24 and 25 include a first pintle 252 extending from thesheath 168 adjacent to cutter 158. The support 250 may also include anda second pintle 254 opposed to the first pintle 252, and also extendingfrom the cylinder 168. The first pintle 252 or the second pintle 254 orboth may include a stop ring to assist in the support of the cuttingtool assembly 226. As shown in FIGS. 24 and 25 the cutting tool assemblyincludes a stop ring 256 extending from pintle 254. At least one of thepintles, 252 or 254 may be utilized to cooperate with the bearings 172to permit the pivoting of the cutting tool assembly 222 about axis 178as shown in FIG. 16.

Referring now to FIG. 26, an alternative embodiment of the cutting guideof the present invention is shown as cutting guide 356. Cutting guide356 is similar to the cutting guide 156 of FIGS. 20 and 21. The cuttingguide 356 includes a base 376. The base 376 defines convex mountingsurface 382. The cutting guide 356 includes a locating feature 362including, for example, mounting surface 382 as well as pegs 384extending from the mounting surface 382.

The cutting guide 356 further includes a guiding feature 360 in the formof, for example, first support or post 374 and second or outward support320. The supports 374 and 320 are utilized to define inboard bearing 372and outboard bearing 322. The bearings 372 and 320 define longitudinalaxis 378 about which the tool assembly rotates.

Unlike the cutting guide 156 of FIGS. 20 and 21, the cutting guide 356includes both outboard and inboard bearings 372 and outboard bearing 322that are spaced further from each other than the bearings 222 and 172 ofthe cutting guide 156. The bearings 372 and 322 of the cutting guide356, unlike the bearings of the cutting guide 156, are spaced apart sothat the sheath 168 of the cutting tool assembly 156 may be positionedbetween the inward post 274 and the outboard post 320. Since the cuttingtool assembly 226 is positioned between the post 274 and the post 320,the base 276 includes a central opening or aperture 330 through whichthe sheath 168 may rotate and through which the cutter 158 may pass.

Similar to the cutting guide 156, the cutting guide 356 of FIG. 26includes a mounting hole 342 as well as a pair of spaced apart handleholes 316 for use with the left or right hand shoulder.

Referring now to FIG. 27, the instrument kit 100 is shown. The kit 100includes a first portion tool or end mill 110 as well as a exteriorpocket preparing instrument 150. The first portion tool or mill 110 mayinclude a stem or shank 114 to which cutter 112 extends. A centralopening 116 may extend through the cutter 112 and the stem 114.

The exterior pocket preparing instrument 150 may include a cutting guide156 as well as cutting tool assembly 226. The cutting tool assembly 226may include a sheath 168 within, which rotatable tool 158 rotates.

The cutting guide 156 may include a base 176, which defines locatingsurface 182. Cutting guide 156 includes a first feature or guidingfeature 160, which include a bearing 172 for supporting the cutting toolassembly 226. The bearing 172 is supported by a post 174 extending fromthe base 176. The cutting guide 176 further includes a second feature orpositioning feature 162. The positioning feature 162 may include thelocating surface 182 as well as, for example, protrusions in the formof, for example, pin 184. A handle 180 may be utilized to guide thecutting guide 156 into position unto the glenoid.

Additional items may be a part of the instrument set on kit 100. Forexample, the instrument set 101 may include a pin 100 for use withpositioning the end mill 110. The instrument 110 may further include adrill guide 130 for preparing a first peg opening 146. The first drillguide 130 may include a base 132, which defines an opening 136 forreceiving the alignment pin 100 as well as a support surface 134. Adrill 144 may be utilized with the first drill guide 130 and pass therethrough. A handle 140 may be utilize to properly position the firstdrill guide 130.

The instrument kit 101 may further include an additional drill guide196. The drill guide 196 may be utilized for preparing the second peghole 198. The second drill guide 196 may include a base 202 from whichsecond peg hole alignment pin 208 extends. The base 202 is adapted forreceiving and guiding drill 200 to form second peg hole 198. Drill guide196 may include a handle 204 for positioning the guide 196.

The instrument kit 100 may further include an additional drill guide 390for preparing additional peg holes for the glenoid component. Forexample, the instrument kit 100 may include drill guide 300 having abase 392 including for example, first opening 394 and second opening 396for receiving a drill to prepare additional peg holes. Drill guide 390may include a handle 398 for assisting in positioning the guide 390.

Referring now to FIG. 28, humeral prosthesis 400 is shown for use with aglenoid pocket 410 prepared by the instruments of the present invention.The prosthesis assembly 400 includes a humeral prosthesis 408 positionedon humerus 404. The humeral prosthesis 408 includes a head 406 extendingfrom the humeral stem 402. The humeral stem 402 and humeral head 406form humeral prosthesis 408. Glenoid component 20 cooperates with head406 of the humeral prosthesis 408. The glenoid component 20 ispositioned in prepared pocket 410 including prepared surface 122 as wellas mounting pocket 152 formed on scapula 40 with the instruments of thepresent inventions.

Referring now to FIGS. 29, 30, and 31, another embodiment of the presentinvention is shown as cutting tool assembly 526 of an instrument set 500is shown. The cutting tool assembly 526 includes a sheath or housing568. The sheath 568 is generally cylindrical and hollow. A millingcutter body 558 is rotatably fixed within the sheath 168. The millingcutter 558 extends from the distal end 530 of the body 528. The body 528is slidably engagable with stem 534. The body 528 defines a femalecutter connection 594, which engages with male cutter connection 592formed on stem 534. The male cutter connection 592 may include a groove596, which mates with a helical spring 598 positioned in the femalecutter connection 594 of the milling cutter body 528, the sheath 568,and the stem 534 may be made of a metal. If made of a metal, the metalmay be a cobalt chromium alloy, a stainless alloy, or a titanium alloy.The bushing 590 may also be made of any suitable, durable material butpreferably is made of a material that provide a bearing function for thecutting tool assembly. For example, the bushing 590 may be made of aplastic, for example, acetal copolymer.

The milling cutter 558 may have any suitable shape and may include aplurality of flutes 544 including the cutting edges 546. Any number ofplurality of flutes 544 may be utilized. For example, and is shown inFIG. 29-31, four equally spaced apart flutes 544 may be utilized.

The cutting tool assembly 526 may include a connector 542 for connectionwith the driving tool, for example, a power drill 106.

The stem 534 may have any suitable shape and may include a shaft portion532 positioned between the connector 542 and male connector 592. Acollar 588 may be positioned between the shaft 532 and the maleconnection 592. The collar 588 serves a axial seat for the bushing 590.

Referring now to FIG. 32, an alternate embodiment of the cutting guideof the present invention is shown as cutting guide 556. The cuttingguide 556 is similar to the cutting guide 156 of FIGS. 20-21. Thecutting guide 556 is designed for use with the cutting tool assembly 526of FIG. 29-31. The cutting guide 556 includes a base 576. The base 576defines convex mounting surface 582. The cutting guide 556 includes alocating feature 562 including, for example, mounting surface 582 aswell as pegs 584 extending from the mounting surface 582.

The cutting guide 556 further includes a guiding feature 560 in the formof, for example, a first support or post 574 and a second post orbearing 520. The support 574 and 520 are utilized to define bearing 572and stop 522. The bearing 520 defines longitudinal axis 578 about whichthe tool assembly rotates.

Referring again to FIG. 30, cutting assembly mounting mechanism 555 isshown. The cutting assembly mounting mechanism 555 cooperates with theguiding feature 560 of the cutting guide 556 of FIG. 32. The cutterassembly mounting mechanism 555, as shown in FIG. 30, includes a stopring 552 extending outwardly from pintle 554. The pintle 554 is designedto rotate on bearing on trunnion 572 of guiding feature 560 of thecutting guide 556 of FIG. 32. The stop ring 552 is positioned betweenstop 522 of the first post 574 and the second post 520.

The milling cutting body 528, the sheath 568, and the stem 534 may bemade by an suitable, durable material. For example, the milling cutterbody 528, sheath 568 and stem 534 may be made of a metal, for example, acobalt chromium alloy, a stainless steel alloy, or a titanium alloy.

Referring now to FIG. 33, a method of performing shoulder arthoplasty ismethod 600. The method 600 includes first step 602 of determining apreference location on the glenoid and a second step 604 and preparing alocation feature in the glenoid corresponding to reference location.

The method 600 further includes a seventh step 614 of providing aglenoid implant and an eighth step 616 of implanting the glenoid implantinto the cavity.

The method 600 further includes a third step 606 of providing a cuttingguide and a fourth step 608 of securing the cutting to the locationfeature. The method 600 further includes a fifth step 610 of providing acutter and a sixth step 612 of preparing a cavity with the glenoidcutter and using the cutter guide to at least partially control theposition of the cutter as prepares the cavity.

According to the present invention and referring now to FIG. 34, anotherembodiment of the present invention is shown as instrument set 700. Theinstrument set 700 is similar to the instrument set 101 of FIGS. 13-25and also similar to the instrument set 500 of FIGS. 29-32. Theinstrument set 700 includes a cutting guide 756 similar to the cuttingguide 556 of FIG. 32. The instrument 700 further includes a cutting toolassembly 726 for cooperation with the cutting guide 756. The cuttingtool assembly 726 is generally similar to the cutting tool assembly 526of FIGS. 29-31.

The instrument set 700 shown in FIG. 34, is adapted for use in preparingmounting pockets 752 and 753 on the tibia 701. The mounting pocket 752and 753 may be used to receive a portion of a unitary tibial (notshown), tray as part of a knee prosthesis (not shown), or the mountingpocket 752 may be used to receive a medial partial tibial component (notshown) of a partial knee prosthesis (not shown). For example, themounting pocket 753 may be adapted for receiving a lateral partialtibial component of the partial knee prosthesis.

The cutting tool assembly 726 is mountable on the cutting guide 756. Thecutting guide 756 may include a base 776 including surface ???? 782 forcooperation with prepared surface 751 of the tibia 701. The preparedsurface 751 may be prepared by tools similar to that of the instrumentset 101 of FIGS. 13-25.

Supports in the forms of bearing 720 and post 774 may extend from thebase 776.

The cutting tool assembly 726 may include a cylindrical body 768 whichis hollow. A tool cutter 758 may be rotatably fitted within the cylinder768. The tool cutter 758 may be connected to, for example, power source706. The power source 706 may be in the form of, for example, a powerdrill. A pintle 754 may extend from the cylinder 768. The pintle 754rests on trunnion 772 formed on the bearing 720. A stop ring 752 mayextend outwardly from the pintle 754. The stop ring 752 is constrainedbetween bearing 720 and post 774 of the cutting guide 756. The stop ring754 and the pintle 754 comprise the mounting mechanism 755 of thecutting tool assembly 756. The mounting mechanism 755 of the cuttingtool assembly 726 cooperates with first feature 760 of the cutting guide756. The first feature 760 includes the bearing 720 and the post 774.

The cylinder 768 of the cutting tool assembly 726 pivots about trunnion776 providing a path for the tool cutter 758 so that the tool cutter 758may create mounting pockets 752.

It should be appreciated that the cutting guide 756 may be positioned ina post position on the tibia 701 opposed to that position as shown inFIG. 34. In such a second position the cutting tool 758, as shown inphantom, in positioned over the second mounting pocket 753. By doing so,the cutting tool assembly 726 and the cutting guide 756 may be used toprepare the first mounting pocket 752 as well as the second mountingpocket 753 of the tibia 701.

It should be appreciated that the instrument set of the presentinvention may be utilized to prepare pockets or portions of a jointwithin the body to prepare a surface for mounting a prosthesis. Forexample, the instrument set of the present invention may be utilized toprepare a surface on the femur, the humerus, the ulna, the radius, orthe tibia.

Although the present invention and its advantages have been described indetail, it should be understood that various changes, substitutions, andalterations can be made therein without departing from the spirit andscope of the present invention as defined by the appended claims.

We claim:
 1. A method for performing arthroplasty on a glenoidcomprising the steps of: determining a reference location on theglenoid; preparing a location feature in the glenoid corresponding tothe reference location; providing an cutting guide, the cutting guidehaving a first feature and a second feature, the first feature includinga housing, the guide further including a base and a restrainingcomponent, said base including the second feature, the second featureincluding a convex surface for contact with the joint surface and therestraining component operably associated with said base and includingthe first feature, the restraining component being removably coupled tothe housing; securing the cutting guide to the location feature;providing a cutter; preparing a cavity in the glenoid with the cutter,using the cutting guide to at least partially control the position ofthe cutter as it prepares the cavity; providing a glenoid implant; andimplanting the glenoid implant onto the cavity.
 2. A method forperforming arthroplasty on a glenoid as in claim 1, wherein thedetermining step comprises inserting a drive pin into the scapula.
 3. Amethod for performing arthroplasty on a glenoid as in claim 1, whereinthe preparing a location feature step comprises drilling a hole in thescapula.
 4. A method for performing arthroplasty on a glenoid as inclaim 1: wherein the first feature of said guide is defined by a wall insaid guide forming a cylindrical opening; and wherein said toolcomprises a rotatable tool fitted to the cylindrical opening.
 5. Amethod for performing arthroplasty on a glenoid as in claim 1 whereinthe first feature of said guide is moveable with respect to said guide.6. A method for performing arthroplasty on a glenoid as in claim 1,wherein the second feature of said base further comprises a protrusionextending from the convex surface for cooperation with the joint.
 7. Amethod for performing arthroplasty on a glenoid as in claim 1, whereinsaid restraining component comprises a bearing; and wherein said tool ispivotably attached to said bearing.
 8. A method for performingarthroplasty on a glenoid as in claim 7, wherein said bearing defines abearing centerline of rotation and wherein said centerline is generallyparallel to the convex surface of said base.
 9. An instrument as inclaim 1, further comprising a handle for positioning the instrument withrespect to the joint.